An image forming apparatus such as a copying machine or a composite machine includes a fixing device to fix a toner image on a sheet at the time of printing. In order to stably perform printing on the sheet, the heat capacity of the fixing device must be large to a certain degree. Thus, warming-up of the fixing device requires a certain time.
However, the time required to warm up the fixing device is shortened by recent technical development. Thus, according to the peripheral environment and use state of the fixing device, there is a case where the warming-up of the fixing device is ended before a control system and the like of the image forming apparatus start up. In this case, power for keeping the temperature of the fixing device is wastefully consumed until the control system starts up.